Gel-like crosslinked organopolysiloxanes are used, for example, in cosmetics and in junction coatings for electrical wiring, but are all solid substances that lack flowability. Hence, they do not dissolve in solvents and so a long grinding operation is required to formulate these in cosmetics or resins.
Silicone oil dispersions of silicone gels are used in cosmetics. Such products are obtained by first creating a solid silicone gel via an addition reaction, and then grinding up the gel while dispersing it in a silicone oil. This production method is troublesome to carry out. Moreover, in the solid silicone gel, even if unreacted functional groups are present near the regions that have become solid due to the reaction, the reaction proceeds no further. As a result, even when the same starting materials are used, the crosslink density differs each time that production is carried out, making the physical properties difficult to control.
In plastics, a silicone oil or silicone gum having a high degree of polymerization is dispersed in the resin and used to increase the flowability during molding or for such purposes as to prevent blemishes or to confer slip properties. Silicone oils with a low degree of polymerization have a flowability increasing effect and exhibit excellent slip properties, but because the silicone oil bleeds out onto the surface, the surface becomes slippery. Hence, gum-like silicones having a high degree of polymerization are used, but it takes a lot of trouble to uniformly disperse such silicones, such as by masterbatching beforehand. Moreover, because most of the silicone added gets buried within the resin, only a portion takes part in action at the surface, resulting in a poor efficiency. On the other hand, when a solid silicone gel or resin is used, given the many ingredients that accumulate within the resin and also their poor compatibility with the resin, dispersion is poor, which often lowers the mechanical strength. Moreover, the surface modifying effects are poor.
No methods for synthesizing compounds having physical properties intermediate to those of silicone gels and silicone oils have been reported in the literature.
Also, in order to prevent bonding and sticking between base materials of paper, plastic or the like and pressure-sensitive adhesive materials, a cured film of a organopolysiloxane composition has hitherto been formed on the surface of the base material, thereby imparting release properties. The method of forming a peelable film by an addition reaction provides excellent curability and can accommodate a variety of peeling property requirements ranging from low-speed peeling to high-speed peeling, and thus is widely used as a method of forming a cured film of organopolysiloxane on a base material surface.
The types of organopolysiloxane compositions used in this method of forming a peelable film by an addition reaction include one type obtained by dissolving an organopolysiloxane composition in an organic solvent, another type obtained by dispersing an organopolysiloxane composition in water using an emulsifying agent so as to form an emulsion, and a solventless type in which the composition consists solely of organopolysiloxane. However, because the solvent type has the drawback of being harmful to the human body or the environment, from the standpoint of safety, a switch is underway from solvent-type compositions to solventless-type compositions. Also, because solvent-type and emulsion-type compositions require the removal of solvent or water at the time of application, the transfer roller used for application cannot be set to a high speed. In addition, in solvent-type compositions, high-speed application is impossible owing also to the danger of ignition. In the case of solventless-type compositions, because there is no solvent to be removed by evaporation and the flash point is high, during mass production, high-speed application is carried out, increasing the productivity. However, when carrying out the high-speed application of solventless-type compositions, misting arises. The various mist suppressants mentioned below have been proposed in order to solve this problem of misting.
The mist suppressant in JP-A 2006-290919 (Patent Document 1) is the product of a condensation reaction between a diorganopolysiloxane capped at both ends with silanol groups and an organohydrogenpolysiloxane using a tin catalyst.
The condensation reaction is difficult to control and so there are marked differences by lot in the degree of polymerization of the reaction product. Although the mist-suppressing effect increases at a higher degree of polymerization, a gel-like product forms, making mixture into a silicone for release paper difficult. Conversely, at a low degree of polymerization, mixture into silicone for release paper is easy, but the mist-suppressing effect decreases and the migration of unreacted product sometimes occurs, which may result in a lower peel strength. Also, a concern with tin catalysts is their toxicity; when used in addition-curable silicone compositions for release paper, they act as poisons for platinum catalysts and inhibit curing, making their use undesirable.
The mist suppressants in JP Nos. 5033293 and 5033294 (Patent Documents 2 and 3) are obtained by adding, to a solventless silicone composition for release paper, a compound prepared by reacting beforehand, in the presence of a platinum catalyst or the like, a mixture wherein either an alkenyl group-containing siloxane or an organohydrogenpolysiloxane is present in large excess (SiH group/alkenyl group ratio is at least 4.6, or alkenyl group/SiH group ratio is at least 4.6). These patent publications relate to addition reaction products endowed with a mist-suppressing effect; having one of the starting materials be present in a large excess lowers the molecular weight of the addition reaction product, enabling the viscosity to be held down. Also, following the cure, surplus functional groups react with the silicone composition for release paper, suppressing migration.
However, due to the platinum catalyst that remains within the mist suppressant, when the SiH group/alkenyl group ratio is 4.6 or more, there is a high danger of dehydrogenation occurring over time. This may also have an influence on the cure, and irregularities in the crosslink density depending on the site may arise. On the other hand, when the alkenyl group/SiH group ratio is 4.6 or more, the SiH group/alkenyl group ratio of the silicone for release paper becomes low and the crosslink density changes, resulting in a change in peel strength.
The mist suppressant in JP-A 2006-506509 (Patent Document 4) is a compound obtained by partially crosslinking a vinyl group-containing MQ resin with a partially substituted hydrido-silicone produced by incompletely reacting a long-chain olefin with an organohydrido-silicon compound.
Patent Document 4 sets out to render a Q unit-containing siloxane into an oil-like substance. When MQ units are added to an organohydrido-silicon compound, depending on the lot, gelling sometimes arises even when the formulation is the same, thus making the viscosity difficult to control. Also, in the addition reaction, the degree of conversion for the vinyl group-containing MQ resin is low and, following reaction completion, the reaction sometimes proceeds over time, resulting in a higher viscosity. On trying to increase the degree of conversion for the vinyl group-containing MQ resin in the addition reaction, the amount of platinum catalyst rises, making it impossible to include the mist suppressant beforehand in the silicone composition for release paper and worsening the pot life even when the mist suppressant is added at the time of use.
JP-A 2006-506510 and JP-A 2006-508206 (Patent Documents 5 and 6) relate to star-branched polymers as mist suppressants for coatings. Star-branched polymers are reaction products obtained by adding a vinylsiloxane or an unsaturated functional group-containing organic compound to the product of an addition reaction between a modified organohydrogenpolysiloxane having silicon-bonded hydrogen atoms and a Q unit (SiO4/2 unit)-containing vinylsiloxane.
A gel tends to form in these reaction products and, depending on the adhesiveness and olefin chain effects, the peel strength sometimes becomes high.
The mist suppressant of JP-A 2010-150537 (Patent Document 7), which is included in a silicone composition for release paper, is a polymer obtained by an equilibration reaction between a branched organopolysiloxane oligomer containing Q units (SiO4/2 units) and a diorganosiloxane oligomer.
A Q unit-containing organopolysiloxane oligomer is difficult to produce while controlling the molecular weight, and so there is a large disparity by lot in the molecular weight. Hence, effecting uniform dispersion by equilibration is difficult, and constantly obtaining a uniform equilibrated compound is a challenge.
JP-A 2010-502778 (Patent Document 8) includes, as a mist suppressant in a silicone-based coating ingredient (silicone composition for release paper), a branched polysiloxane component produced from a copolymer of: (a) an organosilicon compound having at least two unsaturated hydrocarbon functional groups per molecule and (b) an organosilicon compound having at least two silyl hydride functional groups per molecule.
This reaction product often forms a gel, and the presence of a silicone gel gives rise to surface irregularities and unevenness in the coating film. Also, because platinum catalyst remains in the branched polysiloxane component, when silyl hydride functional groups remain within the branched polysiloxane component, dehydrogenation reactions arise during storage, as a result of which the container may swell or, in extreme cases, burst. Moreover, in formulations where the amount of regulator is low, this sometimes causes addition reactions to arise in the silicone-based coating ingredient during dispersion.